液桥力和范德华力作用下细颗粒沉积动力学研究

Particle with aerodynamic diameter less than 2.5μm is called fine particulate matter, usually denoted as PM2.5. Presently, PM2.5 is one of the important factors which lead to the reducing of atmospheric visibility and the regular appearance of haze weather or any other major environmental issues. The purpose of this work is to explore the microscopic mechanism of fine particles deposition considering both liquid bridging and Vander Waals forces with the methods of experimental techniques, theoretical analysis and numerical simulation. Then, the multi-scale characteristics of fine particles’ deposition are investigated with multi-scale simulation methods. Based on the experimental system of particle-surface impact, the microscopic mechanism between fine wet particle interactions is discussed and finally a dynamic model for impact was developed considering the energy dissipation. Furthermore, microscopic particle image processing methods are investigated to achieve quantitative particles’ speed, the number of particle deposition and the length of particles’ chain and so on near a single fiber. The research on the deposition kinetics of fine particles will firstly reveal the impact of the interaction between the particles’ deposition on the body itself and the entire flow field which is previously neglected. Secondly, it will form systematic related multi-scale characteristic of the fine particle deposition and develop a relatively perfect multi-scale DEM model for fine particles’ deposition in multiphase flow system. Finally, this work will propose effective strategy for the control of fine particles and provide the theoretical foundation of fine particles’ efficient removal and control in the national economy and social development.

细颗粒物是指空气动力学直径小于2.5μm的颗粒物(PM2.5)。目前，PM2.5是导致我国大气能见度降低和阴霾天气等重大环境问题的重要因素。本项目通过实验测试、理论分析和数值模拟三大手段，深入探索液桥力和范德华力作用下细颗粒沉积的微观机理和基本规律，用多尺度模拟方法探索细颗粒沉积的多尺度特性；基于颗粒撞击实验系统研究细湿颗粒间相互作用的微观机理，建立考虑耗散机制的碰撞动力学模型；研究显微粒子图像处理方法，实现单纤维附近颗粒速度、沉积数目和颗粒链长度等参量的定量测量。本项目关于细颗粒沉积动力学的研究将在微观层面上揭示以往被忽视的沉积颗粒间相互作用对沉积体和整个流场的影响，形成比较系统的有关细颗粒沉积的多尺度特性的新知识；建立多相流系统中细颗粒沉积过程比较完善的多尺度DEM模型；提出对细颗粒进行有效控制的策略和途径，为细颗粒在国民经济和社会发展中高效清除和控制提供基础。

颗粒动力学广泛应用于工业生产中，如电除尘器、循环流化床、过滤器和制造业。最近微尺度颗粒之间的碰撞粘附过程的研究尤为重要。通过实验的方法研究颗粒与平板碰撞过程中研究相对湿度和颗粒物性对碰撞特性的影响。结果表明法相恢复系数随相对湿度的增加而减小。电除尘器中，颗粒通过放电极线带电，由于电场力的作用向集成板运动。研究了颗粒在电场力作用下的流动状态。结果表明沉积效率随入射速度的减小而增加。